Fluid blast circuit breaker



J. M. CUMMING FLUID BLAST CIRCUIT BREAKER March 21, 1950 4 Sheets-Sheet 1 Filed Sept. 12, 1946 0// Le ve/ Insu/a f/on INVENTOR ATTORNEY -fame5 M Cumming Q BY 5{/ March 21, 1950 J. M. CUMMING 2,501,318

FLUID BLAST CIRCUIT BREAKER Filed Sept. 12, 1946 4 Sheets-Sheet 2 INVENTOR James M Comm/09:

March 21, 1950 J. M. CUMMING 2,501,318

FLUID BLAST CIRCUIT BREAKER' Filed Sept. 12, 1946 4 Sheets-Sheet 3 [50 M'fh 50951055, 5) 53 59 3 100 Q WITNESSES: Q. 50 INVENTOR f4 Q James/W. 60mm M29:

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0" z a Z BY Cyc/e5 & l1

ATTORNEY March 21, 1950 J. M. CUMMING 2,501,318

FLUID BLAST CIRCUIT BREAKER Filed Sept. 12, 1946 4 Sheets-Sheet 4 Bi /0. IX

WITNESSES: INVENTOR 5Q 7%214 IX J'amgs A4. C umm/hg z. A. M

GLa fZW/M ATTORNEY Patented Mar. 21, 1950 "UNITED STATES PATENT OFFICE FLUID BLAST CIRCUIT BREAKER JamcsM. Cumming, Turtle Creek, :Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation'of Pennsylvania Application September 12,19.46,'Serial No. 696357 3 11 Claims. 1

This invention relates to circuit interrupters, in general, and, more particularly, to arc-extinguishing structures therefor.

A general object of my invention is to provide an improved arc-extinguishing unit in'which the pressures within the unit are controlled to effectively' bring about circuit interruption.

A-more specific object is to provide a circuit interrupter embodying one or more arc-extinguishing units inwhich valve means are incorporated to control the venting to or exhaust from the interrupting chamber of fluid directed from the pressure-generating chamber. Preferably, the valve means isresponsive to the pressure within the pressure-generating chamber.

A further object is to provide an improved arc-extinguishing structure of the type having pressure-generating, intermediate and movable contacts in which the interrupting arc established between the intermediate and movable'contacts is subjected to more effective fluid flow and pressure conditions than has been obtained heretofore.

Further objects and advantages will readily become apparent upon a reading of the following specification, taken in conjunction with the drawings in which:

Figure 1 is a side elevational view, partly in section, of a circuit interrupter embodying my invention and shown in the closed circuit posi- .tion;

Fig. 2 is an enlarged vertical sectional view through the right-hand arc-extinguishing unit of Fig. 1, the contacts being shown in the partially open circuit position, low current conditions being assumed;

Fig. 3 is a fragmentary enlarged vertical sectional view taken along the line III--Ill of Fig. 4;

Fig. 4 is a sectional view taken along the line IV-IV of Fig.2;

Fig. 5 is a modified type of arc-extinguishing unit similar to that set forth in Figs. 1-4, except that a modified type of disconnecting arrangement is provided;

Fig. 6 is a curve showing the advantages of employing my invention;

Fig. 7 is a modified type of arc-extinguishing unit in which valve means are only employed in the inlet passage means;

Fig. 8 is a fragmentary vertical sectionalview taken along the line VIIIVIII of Fig. I;

Fig. 9 is a sectional view of a modified type of arc-extinguishing unit having valve means both disposed intheinlet passage means and'also in- 2 the exhaust passage means taken on the line IX--IX of Fig. 10; and

Fig. 10is a' fragmentary sectional view taken along the line 'X--X of Fig. 9.

Referring to the drawings, and-more particularly to Fig.1, the reference numeral I designates a tank inwhich is "disposed a suitable arc-extinguishing'fluid 2, in this instance circuit breaker oil, filling the tank I "to the level indicated. Depending from the cover 3 of-the tank I are two insulating bushings 4 of identical construction, carrying-attheir lower ends identical arc-extinguishing'units generally designated by the reference'numeral 5 and electrically interconnected by'a conducting-bridging member 6 actuated vertically in-a reciprocal manner by an insulating operating rod 1.

Referring toFig. 2, which shows moreclearly than Fig. 1 the-internal construction of the arcextinguishing unit '5, it will be observed that I haveprovided 'astationary contact foot casting Q'WhlCh isthreadedly secured as at!) to the lower end'of the terminal stud It, which'passes upwardlyinteriorly through the bushing 4. After the contact foot 8 is threadedly secured in position, it may be clamped in place by bolts (not shown) extending through apertures I i provided in the contact foot "8. The contact foot 8 has off-standing lug portions 12 integrally formed therewith, the latter having apertures l3 provided'therethrough. A-pair of valve rods H!- have their upper extremities serving as guide portions for projecting jupwardly through the apertures I3 of the lug portions lzof contact footB. The body portions of the valve rod l4 constitutingvalve meansextending interiorly within the arc-extinguishing unit "5.

The contactstructure associated with the arcextinguishing unit/5 includes a relatively stationary pressure-generating contact IS, an intermediate contact 16' and a lower movable contact H, the latter constituting an upstanding portion of the-conducting bridging member 6. The stationary pressure-generating contact l5 cooperates with the intermediate contact l6 to establish a 'pressuree'generating arc I8 Within a substantially confined pressure-generating chamber, generally designated by the reference numeral l d. An in terruptin'g are 20 is established between the tip portion'of'the lower movable contact I I and the lower extremity of the intermediate contact It within a vented interrupting chamber generally designatedby the reference numeral 2:. The plate structureiorming the pressure-generating chamber l Sand the vented interrupting chamber 2| is of the type more clearly set forth and claimed in United States patent application Serial No. 465,244, filed November 11, 1942, by Leon R. Ludwig, Winthrop M. Leeds and Benjamin P. Baker, now U. S. Patent 2,406,469, issued August 27, 1946, and assigned to the assignee of the instant application.

Referring more particularly to Figs. 3 and 4, it will be observed that the pressure-generating chamber 19 communicates through inlet passage means, including two vertically disposed fluid passages generally designated by the reference numeral 22 and formed upon alignment of openings provided in the several insulating plates. The fluid passages 22 communicate with a plurality, in this instance three, pairs of inlet passages 23 leading toward the interrupting are and provided by a plurality of inlet plates 23a. After the fluid contacts the interrupting arc, it may pass through orifices 24 provided by a plurality of orifice insulating plates 25 and pass laterally outwardly from the interrupting chamber 2| to the region exterior of the unit 5 through exhaust passage means, including oppositely disposed exhaust passages 26 formed by the cooperation of two identically formed vent plates 21 (Fig. 4). It will, consequently, be apparent that fluid under pressure formed at the pressure-generating arc l8 will be forced downwardly through the two vertical flow passages 22, or inlet passage means, through the inlet passages 23 to contact the interrupting are 20 and pass laterally out of the unit 5 through the exhaust passages 26.

The several plates are held fixedly in position by a plurality, in this instance six, insulating tie rods 28, the disposition of which is more clearly shown in Fig. 4. The tie rods 28 extend longitudinally of the unit 5 and have lock washers 29 together with nuts 30 at their lower ends,

with the upper ends of the tie rods 28 being enlarged as at 3| (Fig. '7) and extending through apertures 32 provided in off-standing lug portions 33 of the contact foot casting 8. Insulating sleeves 34 are disposed between the lower side of the contact foot 8 and a ring-shaped insulating block member 35 which rests upon the upper side of the several plates forming the interrupting chamber or passage 2|. Thus, the several plates constituting the interrupting chamber 2| with the ring-shaped insulating member 35 are secured fixedly in position relative to the contact foot 8.

It will be observed that the substantially confined pressure-generating chamber l9 has a conducting movable pressure plate 38 disposed at its upper end having a plurality of circumferentially disposed apertures 31 therein through which extend the two valve rods [4 and the six insulating tie rods 28. The pressure plate 36 thus is slidably guided by means of the two valve rods l4 and the insulating sleeves 34 surrounding the tie rods 28.

The conducting pressure plate 36 is electrically connected to the contact foot 8 by a flexible connector 38. The pressure plate 36 carries the relatively stationary pressure-generating contact 55. Also, an annular gas relief valve 39 is associated with the pressure plate 36, being springbiased downwardly to its open position by compression springs 40 so that gas collected within the pressure-generating chamber 19 may exhaust from the said chamber through passages 41 provided in the pressure plate 36. The volume of the annular recess 42 within which the annular valve 39 moves is such that during the closing stroke, the volume of the intermediate contact l6 projected into the pressure chamber I9 is compensated by the volume provided by upward movement of the annular valve 39 within the annular operating recess 42. Consequently, there is no tendency for the incompressible oil within the pressure chamber 19 to block upward movement of the intermediate contact I6 during the closing operation of the interrupter.

It will be observed that the two valve rods H are biased downwardly by compression springs 43 disposed between flanges 44 integrally formed with the valve rods I 4 and the lug portions l2 of the contact foot 8. Thus, the valve rods M are biased downwardly so that reduced portions 45 cut in the valve rods l4 do not register with the exhaust passages 26 provided by the vent plates 21. Therefore, in the closed circuit position of the interrupter, as shown in Fig. 1 of the drawings, the exhaust passages 26 are closed by the valve rods i4 and are only opened upon a predetermined pressure within the pressure-generating chamber IS.

The pressure-generating chamber H! has wall means including a plurality of overlapping cylindrical members 45 having their upper ends disposed in a plurality of annular recesses 41 formed in the lower side of the pressure plate 36. Thus, when the expansible pressure-generating chamber l 9 expands by upward movement of the pressure plate 36, the effective area on the pressure plate 36 upon which the pressure within the pressure-generating chamber I9 acts is progressively increased by successive uncovering of the ends of the cylindrical members 46. Thus, the spring pressure is constant during the operation because of the design of the chamber top which works in a series of cylinders, exposing a variable area to the pressure as the top lifts. The flexibility in the chamber top is also used when the interrupter is closed to supply contact pressure. This is possible because of the short travel necessary for that function.

It will be observed. that the valves l4 shut off exit of oil or gas from the unit 5 until the valves 14 are opened by pressure within the pressure chamber l9. This storing of energy in the grid until such time as it reaches anything from five to ten atmospheres before the valves I 4 are opened superimposes pressure on the oil which surrounds the interrupting are 23 holding it to a minimum size, whereby it can be more easily interrupted. The use of this high pressure combination with sudden release thereof will make the interruption of arcing over a longer range from low to high current possible. Previous designs of interrupter have used pressure are energ to push the oil into the are, but instead of holding that pressure, allow probably fifty percent of the pressure to escape through the open exhaust ports thus lengthening the time necessary to build up sufficient pressure to take care of interrupting low currents. In the case of extremely low currents where insufiicient pressure may be generated to open the exhaust port valves I4, the full pressure will be behind the flow of oil which will blow through the opening 48 left by the moving contact I! when it leaves the unit 5. This condition is shown in Figs. 2 and 3 where very low current conditions are assumed and where the pressure within the pressure chamber I9 is insufficient to cause appreciable opening of the valves M to open the exhaust passage means 26.

The operation of my improved interrupter will now be explained. In the closed circuit position the electrical circuit "includes terminal stud '10,

- contact foot 8; flexible.-conne'ctor 3B; conducting i pressure plate "36,- -'stationary bontact |5,tinterm'ediate contact 1 6 through "lower movable con- "tact "I and acrossthe conducting' bridging memher 6 tothe other arc-extinguishingunit 5 of the "interrupter.

*otherunit 5 in an identical mannerwith its pas- Thecircuit extends through the sage "through the righthand-un-it 5. l When it is desired to open the electrical circuit "passing "throu'ghthe interrupter or inre'sponse to'ove'rload conditions existing in theelect'rical circuit controlledby the interrupter, suitable mechanism "-(not 'shown) is'actuable to cause downward movement oftheinsulating operating rod l. The.

' downward movement of the operating rod 1 causes corresponding downward movement of-the conducting bridge 6' and-the lower movable conwithin the substantially confined pressure-gem; crating chamber 19. *When the flange 50 secured to andmovable Withthe intermediate contact i6 strikes the-shoulder portionSl aiforded by the insulating plate 52,- the intermediate contact I6 will cease its downward movement. The consequent separation between the lower movable contact ll'and the lower extremity of the intermediate contact l6 will establish an interrupting are '20 within the interrupting chamber or passage 2|. Fluid underpressure from the pressure-gener- "ating are 18 will flow downwardly through the "vertical flow passages or inlet'passage'means 22,

plate 35.

more clearly shown in Figs; 3 and4pto passradh ally inwardly toward the "interrupting-arc 20 through a plurality of pairs of inlet passages 23.. After contacting the interrupting arc -2ll,"the fluid passes through the orifices 24 provided by the orificeinsulating plates 25 to'pass out the exhaust passages 2t, assuming that'the valve rods 14 have raised sufiiciently to permit opening of'the exhaust passages'ifi. This "condition? however, is not assumed in Figs. 2 to 4, these figures merely assuming the current being interrupted to be so low as to causeinsufficient pressure within the chamber I9 to cause opening of'the valverods 14.

'The amount of pressure generated within the pressure-generating chamber I!) will determine the amount of upward movement ofthe pressure The pressure plate 36 is; of -course, biased downwardly by the compression springs 43 which also biasthe valves 14 to their closed-position. As the pressure plate" 36' moves upwardly, it successively uncovers the upper "ends of the cylindrical members 46 to thereby'permit "an increasingly greater cross-sectional area of the pressure plate36 to be acted upon. Thus, the spring pressure exerted by the compression springs 43 as these springs collapse is offset by the'increasing area upon whichlthepressure acts against the pressure plate 36.

Fig. 6 shows a graph which explains thebenefits'in time saving-where no loss in generated pressure is allowed. "This curve" is'representedby the reference numeral 53. The 'curve 54'represents the-condition which exists wherev approximatch fifty'percent' of thepressur: is. allowed to escape through open exhaust ports. From this graph it will beapparent that the interrupting time is" reduced" by approximately half because of the provision or the valve control 4 whi'ch" clo'se'l the exhaustpassages 2B until" a predeter- 1 "mind pressure exists within the pressure=gencrating chamberl 9.

? "Figi: 5 shows a construbtion' 'in which the lower end -bf theinterrupting passage 2| isnotop'ened upon continued downward movement of thelower movable-contact i1. In this'case thelower'mov- "able contact I l has-amid'entical construction and functions the same as the lower movable contact l0 1 I I of Fig? 2* except that it has a disconnect porti'ori 55 which 'is' enga'ged bya movable disconnect "contacfiiii which'is disposed at the-extremity of the conducting bridging mernber 6. The downwaid movement of-themovable *co'ntact ll -is determinedby-afiang 61 secured thereto'and movable-therewith v hich strikes stop lugs" Wsecured by screws-59 to'the bottom plate- '60 01 the'g'ridor unit-5. with thisconstruction the pressure w-ithin the interrupting chamber 2 I is not permitted tobe'relieved by unplugging of the interrupting passage 2 l bywith'draw'ab of the'mov'able contact "ll-entirely from-the'unit 5. T-he-presence of the m'ov able contact I! in the low-er end-ofthe interruptingpassage 2 l maintains the pressure'h-igh within the interrupting passage 2 l which is beneficial where-very low currents'aresbeing interrupted 1 of not sufiicient magnitude to cause raising of the valve rods 14* andcons'equent opening 'ofthe exhaust passages 26.

It will, of course,be apparent'tothose skilled in the art that continued downward movement of the conducting cross member fi provid'es a disconnect gap between' the disconnect portion 55 -"of the" movable contact l1 and the movable dis connect contact ifi'in 'the fully open circuit position of the interrupter (not-shown). Thus,-in "Fig"- 5 l showa "modified construction in which the lowerend of the interruptingpassage lI is "not-vented near the end of the opening opera- 9 tion. -As mentioned previously, this has distinct advantages in the interruption of very lo'wamperagecurren'ts where insufficient pressure is'generatedat the pressure-generating are 'l 8 w-ithin the pressure chamber 19.

Figs." Wand 8 show a modified construction of arc-extinguishing unit 1 generally 'desi'gnated by the reference numeral 6 l in which the valve rods are omitted and the exhaustpa'ssages ZS-fare open at all times, as 'clearly shown in' Fig. 8.

. However; in this modified construction, Iprovide v'alve'rods '62 responsive tothe pressure within '-the pressure generating chamber [9 whichi c'on- -'trol the opening of the inlet passage": means. 22 interconnecting -the pressure-generating: .chammber "IS-with the interrupting chamber 2|. The

" valve rods'tz" are of generally similar construc- "t'ion to the valve' rods Ill-previously describ'edfin "connection with Figs. 1-4.

'Thusthe valve rods 62 have heads 63 integrally (20' formed' therewith which are responsive 'to upward "-movement of'the' pressure plate 36 and'hence're- -sponsive to the pressure within the pressuregenerating chamber l9. 'The valve rods 62 controlling the inletpassage means 22 haveannular o5 reduced sections 64 formed'therein and are biased downwardly by compression springs 43 which have a similar "'function' to "the compression springs 43 of the valve rods l4des'cribedin'connection' with" Fig. 2. Thus, 5 the compression I springs 43' of Figs '1 not only bias the-valve rods '62 1 toward their closed position -but also" bias zthe pressure plate 36downward1y against the cylin- *driealmembers' 46.

Itwill" be apparent that-in thisembodiment of 15 tmy 'invention' the fluid directed from the pressure generating arc l8 toward the interrupting are 20 within the inlet passage means 22 is controlled by the movement of the valve rods 62 which are responsive to the pressure within the pressuregenerating chamber Hi. When the pressure is sufiicient within the pressure chamber I9 to cause upward movement of the pressure plate 36, this will raise the rods 62 to permit opening of the inlet passage means 22 and thereby permit fluid to flow from the pressure arc [8 toward the interrupting are 20 in a manner as set forth previously in connection with Figs. 2-4=. However, in the modified construction of Fig. 7, the exhaust passages 26 are open at all times as indicated in Fig. 8 and, consequently, once the valves 62 are raised, there is permitted free passage of fluid from the pressure arc l8 downwardly through the vertical flow passages 22 radially inwardly toward the interrupting are 20 through the several pairs of inlet passages 23. After contacting the interrupting arc 2i], the fluid passes through orifices 24 and freely out of the unit 6| through the open exhaust passages 26, the latter not being controlled by any valve means whatsoever.

Figs. 9 and show a modified arc-extinguishing unit, generally designated by the reference numeral 65 and incorporating two sets of valve means. The first valve means is of the type set forth in Fig. 7 and consists of a pair of valve rods 82 having an identical construction to the valve rods 62 of Fig. '1. Also, the exhaust passages 2B in the modified type of arc-extinguishing unit 65 are controlled by valve rods l4 having an identical construction with the valve rods Id of Fig. 2. Thus, in the modified unit 65 of Figs. 9 and 10, I have provided a first valve means for controlling the inlet passage means 22 and a second valve means 14 for controlling the exhaust passages 25. The direction of fluid flow from the pressure are 18 toward the interrupting are 28 is the same as previously described; consequently, a further description thereof appears unnecessary for an understanding of this embodiment of my invention.

It will be apparent that in all the constructions the entire grid is stationary and only the pressure plate 38 moves, being guided by the tie rods 28 and the valve rods it and/or 62. Thus, the movable pressure plate 36 is the expandable portion of the pressure-generating chamber l9 and by the expansion thereof controls the opening of the valve rods Hi controlling the exhaust passages 26 or the valve rods 52 controlling the opening of the inlet passage means 22.

It will be apparent that my invention describes a novel use of the pressure-generating arc in a two break type of arc extinguisher wherein the interrupting arc is contained under pressure and held to a minimum size for easy interruption. The invention reveals a way of containing the interrupting are within the grid by the use of valves on the exhaust port which are opened by the pressure generated by the pressure-generating are within the pressure generating chamber. It will also be apparent that the construction of the pressure chamber is such that the top is flexible and controlled by spring pressure.

Preferably, the valves Hi store the energy within the grid until such time as it reaches anything from five to ten atmospheres before the valves M are open. This superimposes pressure upon the oil which surrounds the interrupting are holding it to a minimum size whereby it can be more easily interrupted. The use of this high pressure combination with sudden release thereof will make the interruption of arcing over a longer range from low to high current possible. In the case of extremely low currents wherein insufficient pressure may be generated to open the exhaust port valves I4, the full pressure will be behind the flow of oil which will blow through the opening left by the moving contact when it leaves the grid. The disk valve 39 in the pressure chamber top is so designed that in closing the moving contact [6 moving into the pressure chamber l9 displaces approximately the same amount of oil that the valve chamber 42 will hold when moved up by the closing operation.

Although I have shown and described specific structures, it is to be clearly understood that the same were merely for the purposes of illustration and that changes and modifications may be readily made therein by those skilled in the art without departing from the spirit and scope of the appended claims.

I claim as my invention:

1. In a circuit interrupter, means defining an arc-extinguishing unit, a substantially confined pressure-generating chamber disposed within the unit, an interrupting chamber positioned within the unit, exhaust passage means venting the interrupting chamber to the region exterior of the unit, contact means for establishing a pressure-generating are within the pressuregenerating chamber and an interrupting are within the interrupting chamber regardless of the pressure there-in, inlet passage means interconnecting the two arcs, valve means for opening the said inlet passage means responsive to the pressure within the pressure-generating chamber, and second valve means responsive to the pressure within the pressure-generating chamber for controlling the exhaust passage means.

2. In a circuit interrupter, means for establishing a pressure-generating arc within a substantially confined pressure-generating chamber, means for establishing a serially related interrupting arc within a vented interrupting chamber regardless of the pressure therein, inlet passage means interconnecting the two chambers so that iiuid under pressure at the pressure-generating arc may flow toward the interrupting arc to effect the latters extinction, and valve means responsive to the pressure within the pressure-generating chamber for controlling the opening of the inlet passage means.

3. In a circuit interrupter, an arc-extinguishing unit, means defining an expansible pressuregenerating chamber, means defining an interrupting chamber, means for establishing a. pressure-generating are within the expansible pressure-generating chamber, means for establishing an interrupting are within the interrupting chamber, exhaust passage means venting the interrupting chamber, inlet passage means interconnecting the pressure-generating and interrupting chambers, valve means responsive to the expansion of the expansible pressure-generating chamber for controlling the opening of the inlet passage means, and second valve means also responsive to the expansion of the expansible pressure-generating chamber for controlling the opening of the exhaust passage means.

4. In a circuit interrupter, an arc-extinguishing unit, means defining an expansible pressuregenerating chamber, means defining an interrupting chamber, means for establishing a presssure-generating are within the expansible pressure-generating chamber, means for establishing an interrupting arc within the interrupting chamber regardless of the pressure therein, exhaust passage means venting the interrupting chamber, inlet passage means interconnecting the pressure-generating and interrupting chambers, and valve means responsive to the expansion of the expansible pressure-generating chamber to control the opening of inlet passage means.

5. In a circuit interrupter, an arc-extinguishing unit, a substantially confined pressure-generating chamber disposed at one end of the unit, an interrupting passage leading out of the other end of the unit, a, pressure-generating contact, an intermediate contact cooperable with the pressure-generating contact to establish a pressuregenerating arc within the pressure-generating chamber, a movable contact having a disconnecting portion separable from the intermediate contact to establish an interrupting arc within the interrupting passage, means preventing removal of the movable contact from the interrupting passage, a movable disconnect contact for moving the movable contact to the closed circuit position, exhaust passage means separate from the interrupting passage and leading from the interrupting passage to the region exteriorly of the unit, and valve means responsive to the pressure within the pressure-generating chamber for controlling the opening of the exhaust passage means.

6. In a circuit interrupter, means defining a pressure-generating chamber, means defining an interrupting chamber, contact means for establishing a pressure-generating arc within the pressure-generating chamber and an interrupting arc within the interrupting chamber, regardless of the pressure therein, and valve means other than the contact means responsive to the pressure within the pressure-generating chamber to control the flow of fluid into the interrupting chamber to effect the extinction of the interrupting arc therein.

7. In a circuit interrupter, means including a movable pressure plate defining a pressuregenerating chamber wall means for the chamber including a plurality of overlapping cylindrical portions, and means permitting successive opening of the ends of the cylindrical portions to pro-- vide a progressively greater surface area on the pressure plate upon which the pressure acts as the pressure plate moves outwardly.

8. In a circuit interrupter, means including a movable pressure plate defining a pressure-generating chamber, wall means for the chamber including a plurality of overlapping cylindrical portions, means permitting successive opening of the ends of the cylindrical portions to provide a progressively greater surface area on the pressure plate upon which the pressure acts as the pressure plate moves outwardly, and biasing means for biasing the movable pressure plate inwardly.

9. In a circuit interrupter, an arc-extinguishing unit, means defining a pressure-generating chamber within the unit, means defining an interrupting passage leading out of the unit, a relatively stationary contact cooperable with an intermediate contact to establish a pressure-generating arc within the pressure-generating chamber, a movable contact movable out of the unit through the interrupting passage and cooperable with the intermediate contact to establish an interrupting arc within the interrupting passage regardless of the pressure therein, laterally extending vent means for the interrupting passage, and valve means responsive to the pressure within the pressure-generating chamber to control the opening of the vent means.

10. In a circuit interrupter, means including a movable pressure plate defining a pressure-generating chamber, wall means for the chamber including a plurality of overlapping cylindrical members, means permitting successive opening of the ends of the cylindrical members to provide a progressively greater surface area on the pressure plate upon which the pressure acts as the pressure plate moves outwardly, biasing means for biasing the movable pressure plate inwardly, and a relatively stationary contact secured to the pressure plate.

11. In a circuit interrupter, an arc-extinguishing unit, means defining a pressure-generating chamber within the unit, means defining an interrupting passage leading out of the unit, a relatively stationary contact cooperable with an intermediate contact to establish a pressure-generating are within the pressure-generating chamber, a movable contact movable out of the unit through the interrupting passage and cooperable with the intermediate contact to establish an interrupting are within the interrupting passage regardless of the pressure therein, inlet passage means interconnecting the pressure-generating chamber with the interrupting passage, and valve means responsive to the pressure within the pressure-generating chamber for controlling the opening of the inlet passage means.

JAMES M. CUMMING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 730,704 Read June 9, 1903 2,063,173 Lange Dec. 8, 1936 2,154,515 Leeds et a1 Apr. 18, 1939 2,412,858 Baker et al Dec. 17, 1946 FOREIGN PATENTS Number Country Date 616,174 Germany July 22, 1935 

